Voice-over Internet Protocol (“IP”) (“VoIP”) services use the IP protocol for the transport of voice-related services. By using the shared data bandwidth of the IP network, VoIP offers much cheaper rates particularly on international destinations over traditional dedicated circuit-switched voice service. VoIP can also provide better integration of other data services such as multimedia, context, and video than traditional circuit-switched voice service.
VoIP telephones have been successfully used by many enterprises. Although consumers mostly still use traditional telephones, many also (perhaps unknowingly) benefit from VoIP service for international calls.
The concept of integrating cellular data service with Wireless Fidelity (“WiFi”) data service has recently been available to consumers. This cellular/WiFi integration allows subscribers to roam seamlessly between cellular data services such as GPRS/1XRT and WiFi services, and to use WiFi services whenever available and to use cellular services whenever WiFi services are not available and cellular services are available.
The concept of integrating cellular data service with WiFi has also recently been extended to support VoIP services combining cellular phones and WiFi. A GSM-WiFi telephone has been introduced that allows subscribers to make telephone calls over an available WiFi service, otherwise the telephone functions like a typical cellular telephone. However when a cellular subscriber is roaming and receives a call on his/her cellular telephone, the received call is routed to the subscriber's cellular telephone via the cellular network. This prevents the subscriber from taking advantage of the VoIP and/or WiFi services, and can be particularly costly to outbound roamers who will have to pay for the rerouted leg of the international call. Consequently there is a need to provide cellular VoIP service to roaming cellular subscribers.
There are many mobile or cellular network operators, or providers, in the world, often more than one in a single country. These network operators include, but are not limited to, operators who provide mobility services using a variety of protocols (e.g., GSM, GPRS, 3G, CDMA, TDMA, etc.) or their variants. These network operators provide voice and data services to their own subscribers and to subscribers from other networks. When the network operator provides service to a subscriber from a foreign country, it is referred to as “international roaming”. When the network operator provides service to a subscriber from another network in the same country, it is referred to as “domestic roaming”.
When the subscriber is registered in the network with which it has a direct billing relationship, the serving network is often referred to as the Home Public Mobile Network (“HPMN”). If the subscriber is in a network with which it does not have a direct billing relationship, the serving network is referred to as the Visited Public Mobile Network (“VPMN”), and the subscriber is referred to as an “inbound roamer” by the VPMN. The same subscriber is referred to as an “outbound roamer” by the HPMN. In such a case, the inbound roamers are treated as temporary subscribers from a service availability perspective, while the billing for usage incurred by them is through inter-carrier settlements via the home network of the subscriber. Consequently there is a need to provide cellular VoIP service to inbound and outbound roaming cellular subscribers.